Electron tube and method of making the same



May 17, 1966 J, w. GAYLQRD v 3,251,641

ELECTRON TUBE AND METHOD OF MAKING THE SAME Filed March 27, 1962 A m I 44 4a a; 757 j 4i Il @l- Q Q s dz 3 20k x Z3 27 4 "f/ ZZ l j 24 F' 4 32 z g la fa a j Z 40 I JNVENToR. .96 Jo/m/ M( @1y/0K0 Arran/5y United States Patent O 3,251,641 ELECTRON TUBE AND METHOD F MAKING THE SAME John Wallen Gaylord, Lancaster, Pa., assigner to Radio Corporation of America, a corporation of Delaware Filed Mar. 27, 1962, Ser. No. 182,908 5 Claims. (Cl. S16- 19) My invention relates to electron tubes, and particularly to an improved tube having a tubular cathode and at least one tubular grid, and to a novel and advantageous method of fabricating such tube.

One type of electron tube of appreciably high power output comprises a tubular cathode including a nonforaminous metal Ibase having on the outer surface thereof a coating of electron emitting material. Surrounding the cathode and coaxial therewith are two concentric tubular grids having radially registering slots. The slots may beV produced by electrically eroding axially parallel elongated portions of imperforate grid blanks, after the blanks have been iixed mutually to provide a grid subassembly. One way in which the electrical erosion may be effected is described in U.S. Patent 2,980,984 to M. B. Shrader et al., issued April 25, 1961.

In tubes of the type referred to, some of the electrodes thereof are fixed in desired positions in a mount structure, by interposing a suitably metalized ceramic ring between adjacent flanges on which the electrodes are mounted, a suitable fixing material, such as BT solder being disposed between meeting surfaces of the flanges and ring. BT solder is an alloy consisting by weight of 28% copper and 72% silver. The electrode mount thus loosely assembled, is placed in an oven ywhichis raised to a temperature high enough to melt the solder into intimate engagement with the coated ceramic ring and flanges. After the solder cools, it serves to x the aforementioned parts with respect to each other.

While the fixing technique referred to, may be used for sealings parts that are free from harm by such technique, its use has not been feasible heretofore, for mounting the cathode and its associated heater. As concerns the cathode, this is' for the reason that the lcathode has thereon an emitting coating, usually in the carbonate form, prior to incorporation-of the cathode in the tube structure. The reason for applying the coating before mounting the cathode, is thatv the cathode was inaccessible for application of the coating after it had been mounted in a tube. Such coating would be harmed if subjected to oven heat. In View of this situation, the cathode was atiixed to the tube mount after the grids and anode had been mounted, by the application of localized heat, such as that involved in heliarc welding. The heater was not mounted in the tube prior to the mounting of the cathode, and therefore was the nal element added to the tube structure.

However, while locally applied heat for fixing the cathode and heater in a tube mount has been tolerated heretofore because of necessity, it is not as good yfor tube quality as heat applied to the parts uniformly, as in an oven. One important advantage of oven type heating is that it reduces the likelihood of unrelieved strains in the tube structure.

It is an important object of the invention to provide an improved electron tube structure.

Another object is to provide an improved method of making an electron tube, in which the cathode is fixed in a tube mount by means of oven heating.

A further object is to provide a novel electron tube subassembly comprising a cathode and at least one grid.

Another object -is to provide a novel cathode and method of making the same.

One structural example of the invention is an electron tube having a grooved metal cathode sleeve coated with a 3,251,641 Patented lMay 17, lg

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metal matrix such as sintered particles of nickel. The matrix extends inwardly of the cathode sleeve to provide a circumferentially continuous inner surface having emitting material in the pores of the matrix. The grooves in the cathode sleeve leave circumferentially-spaced regions elongated axially, that is, parallel to the sleeve axis. These regions are occupied solely Iby a thin matrix and the matrix in that region is recessed inwardly from the immediately adjacent, outwardly exposed cathode surface. The thin, recessed regions referred to, comprise substantially the sole emitting-portions of the cathode, and are in accurate radial register with slots in one or more adjacent grids. The resultant structure possesses good beam forming properties and is characterized by increased ruggedness and long life.

An advantageous method of making the tube structure referred to involves mounting and mutually fixing all components of the tube except the cathode heater, to provide a sub-assembly wherein the inner surface of the mounted cathode is accessible through an end opening thereof for the application thereto of a coating of emitting material. After application of the coating, a heater mount is extended into the cathode through the opening referred to and sealed thereacross.

A feature of the invention involves effecting all seals in the-tube structure by oven heating, except the seal involving the heater mount, for uniformity in the several seals and avoidance of objectionable strains in the seal regions.

This is particularly significant in connection with the cathode, in that this method assures cleanliness of this electrode by avoiding handling thereof after heating.

A further feature of the method comprises eroding selected regions of the cathode and one or more grids, after these electrodes have been xed to each other, to provide radially registering eroded `regions in the electrodes men-. tioned.

Another features involves making a cathode of the tubular type by slitting a tubular blank, coating theA inner surface of the slitted portion of the blank with metal particles, and sintering the particles.

Further objects and features of the invention will become apparent as the present description continues.

Referring now to the drawing for a more detailed consideration of an exemplary embodiment of the invention,

FIG. 1 shows an elevation in section, of an electron tube using my invention;

FIG. 2 is a view in cross-section taken along the lines 2-2 of FIG. 1;

FIG. 3 is a cross-sectional View taken along the lines 3-3 of FIG. 1, and shows the top of the cathode;

FIG. 4 is a sectional View in elevation of apparatus employed in carrying out one of the steps of making the cathode;

FIG. 5` is a sectional elevation of a cathode-grid subassembly in operative relation with respect to apparatus v for eroding radially registering areas therein; and

FIG. 6 is a longitudinal sectional View of an anodegrid-cathode sub-assembly associated with apparatus for applying an emitting coating to the inner surface of the cathode.

The electron tube shown in FIG. 1 comprises an an'ode 10, made of copper for example, and having an exhaust tubulation 12. The anode defines a space within which are disposed a screen grid 14, a control lgrid 16, and

the upper surface of the radially extending portion of flange 22 of the screen grid, is disposed a ring 28 made of a ceramic material such as aluminum oxide. The ends of the rings 28 engaging the anode 10 and fiange 22 are suitably metalized with a metal such as molybdenum over which is coated, as by plating, a metal such as nickel for a purpose to be described. Interposed between t-he metal coating on the upper end of the ring 28 and the anode end surface 27, and between the lower end of the ring 28 and the ange 22, is a body of fixing material, such as BT solder which wets the anode end edge surface v27 and the flange 22 as well as the metal coatings on the ring 28, when heated, and rforms a vacuum-tight seal between these elements when cooled.

While `the Iforegoing se-als are satisfactory, they may be improved, for example, by interposing rings 29 (FIG. made of an alloy such as Kovar consisting by weight of 29% nickel, '17% cobalt and the balance iron, between the sealing surfaces of the insulating sealing ring 30 and, respectively, the flange of screen grid 14 and the flange of control grid 16, Such metal alloy more closely approximates the expansion characteristics of `the material of the insulating ring than does the metal, usually copper, of which the anode and ange are made.l

Seals similar to the ones discussed are also made between the fianges 24 and 26 utilizing an insulating sealing ring 32, which may be made of a material similar to that of sealing ring 28. A similar seal is made by means of a 'sealing ring 28 between arrge 22, and the end edge surface 27 of the anode.

The heater 20 in FIG. 1 is mounted on terminal posts- 34, 36. Termina-1 post 36 is fixed to an apertured metal flange 38 fixed to cathode fiange 26. Terminal post 34 is Afixed to a metal flange or plate 40, serving as the terminal lead for lone end of the heater. Interposed between the flanges 38 and 40 is a disk or plate 42 of insulating material such as aluminum oxide, suitably metalized as a forementioned, for sealing to the flanges or :plates 38, 40.

yIn the tube structure shown in FIG. 1, the cathode 18, control grid 16 and the screen grid 14 are shown with openings 43, 44, 46 at their upper ends. These openings are provided on the axes of these electrodes to facilitate jigging the electrodes into concentric relation.

The cathode 18 has a structure comprising a base (core) made of nickel, for example, and having a plurality of spa-ced fingers 48 having an inner surface coated With a matrix 50 of metal particles such as nickel, suitably impregnated with an emitting material such as mixture of the oxides o'f barium, strontium and calcium, as shown in FIGS. 2 and 3. The fingers 48 are in radial-register with the sleeve segments 49, 51 of grids 14, 16. Between the fingers 48, portions of the impregnated matrix 50 are exposed. This arrangement limits electron emission only tothe regions of exposedmatrix recessed between the fingers .48, emission from adjacent regions being blocked by the fingers 48, This structure results in a rugged longlife cathode contributing to a desirable beaming function.

While only four fingers 48 are shown in FIGS. 2 and 3, for clarity reasons, Imany more fingers may be used. In one exa-mple, eighteen fingers were provided. Furthermore, the matrix S0 need not cover the outer surfaces of the fingers 48, as shown in FIGS. l, 2, and 3 but may be restricted only to the inner surfaces thereof and to the regions between the fingers.

The cathode 18 may be made by a technique illustrated in FIG. 4. Thus, a cathode lblank 52, which may or may not be slitted to .provide fingers therein, is positioned inverted [fashion in a jig comprising a container 54 having an embossment 56 in the bottom thereof corresponding in size to the opening 43 in the blank. A rod 58 is positioned within the cathode blank and has a recess 60 for receiving the embossment 56 and for wedging the lower end wall. of the blank between the rod 58 and the bottom wall of cont-aimer 54. i

The rod 58 'should have a smaller diameter than the 4 inner diameter of the cathode blank 52 as shown in FIG. 4 for a reason that will become apparent. While the inne-r diameter of the container 54 is appreciably larger than the outer diameter of the cathode blank as shown, it may be preferable in some cases, to provide a snug fit between the `cathode blank and container.

After a positioning of the cathode blank 52 on the jig 54, 58, as shown in FIG. 4, a quantity of metal particles, such as nickel, are poured into the -annular spaces 62, 64. The nickel particles may be in a commercial-ly available powder form. The portion of the metal particles in space 64 may be determined by a shoulder 65, and by the amount of metal particles poured. If a snug fit exists between the cathode blank and the container 54 the annular space 64 will be eliminated. It is preferable to pour an amount of metal particles so that the volume thereof will result in a body extending axially parallel along what is to be the active portion only of the cathode. However, itis tolerable t-o have the volume of metal particles extend into engagement with the inner surface of the lower end wall of the cathode blank, as shown in FIG. 4, to facilitate manufacture.

After the metal particles have been poured into and compacted in the space 62 alone, or in the two spaces 62, 64, the jig with the parts thereon, is placed in an oven and first heated in wet hydrogen to a temperature of about ll00 C. :for from 15 minutes to one hour for presintering the metal particles. The cathode blank with the metal particles sintered thereto, is then removed from the jig and' subjected toI an oven temperature of about l200 C. in dry hydrogen, for from 15 minutes to one hour, to complete the sintering operation.

The jig is preferably made of an alloy known as Nichrome which consists by weight of from 19 to 20% chromium, 1% iron, 0.25% manganese, 0.l0%-carbon, 0.45% silicon, 0.10% aluminum and the balance nickel. This alloy responds in oxidation to the presence of wet hydrogen. The oxide on the jig facilitates removal of the workpiece therefrom after the first of the aforementioned heat treatments is completed.

The :cathode 'so made is then fixed in a sub-assembly by mounting on a suitable jig (not shown), parts comprising the cathode 18, the control grid 16, screen grid 14 and -metalized ceramic rings 30, 32, with BT solder between the engaging surfaces of these parts, for disposing these parts in accurate coaxial relation. The parts so mounted are then heated in an oven to a temperature of 820 C. for softening the solder between the engaging surfaces of the parts, and brazing the parts together. The resultant brazed sub-assembly 63 is 'shown in FIG. 5.

The brazed sub-assembly 63 is next subjected to an .erosion procedure for removing elongated portions of the two grids, and to form grooves in the cathode. In the event the cathode has not been provided with fingers in -a prior step, the formation of the grooves in the cathode involves complete removal of the material of the cathode blank at the regions of the grooves and also, preferably, a removal of a portion of the sintered body within the cathode blank of said regions. slits already in the cathode base, the sintered body may extend continuously from the inner to the outer surface of the cathode blank through the slits, and the outer portions of the sintered body at the slitted regions are eroded away leaving only a recessed inner shell or layer of sintered material,

The erosion step may be carried out in the manner described in U.S. Patent 2,980,984 to M. B. Shrader et al. and referred to before herein. Thus, las shown in FIG. 5, the cathode-grid sub-assembly 63 is positioned on a sup port 66 within a tank 68 containing a suitable dielectric liquid, such as deionized water, to level 70. Supported to be vertically movable above the sub-assembly 63 referred to, is an eroding broach 72 having teeth or fingers 74 equal in number to the number of eroded regions to be provided in the workpiece. The fingers 74 are disposed If there are in ,a circular array coaxial with the sub-assembly 63, with the fingers 74 extending radially in said array. The fingers 74 have a radial extension for extending through the Atwo grids 16, 14, and partly through the sintered portion of the cathode 18 as it is brought down. The fingers 74 extend a sufficient distance inwardly, toward the center of the array, so as to engage the base portion of the cathode, to remove all except the inner sintered layer. The tool is preferably not lowered beyond the lower extent of the sintered material. The remaining portions of the matrix 5f) which are in radial register with the removed portions of the grids and the base portion of the cathode, suffice for service as the active cathode portions, as will appear in the following.

The selective erosion of the work piece 63 shown in FIG. 5 occurs as the broach 72 is lowered into attempted engagement with the workpiece. Before engagement occurs, however, electrical discharges between the broach and workpiece advance an erosion zone downwardly as viewed in FIG. 5. The erosion may be permitted to proceed to a location slightly above the lower end of the matrix Si). In this way, the matrix covers fully the slits or openings in the cathode blank produced by the broach 72. Consequently, there is no spillage of the emitting material through the cathode during application of an emitting material in a manner to be described. To permit the erosion zone to pass 'below the matrix, as viewed in FIG. 5, would result in exposed openings below the matrix through which coating material might spill during application, and might contaminate the grids.

The electrical discharges referred to, occur in response to a potential difference between the broach 72 and the workpiece, produced by connecting leads 76, 78 to sources of potential difference.

It will be noted that the length of the broach fingers 74 is not affected whether or not the cathode blank 52 (FIG. 4) has been provided with fingers or strips prior to the erosion step. Since .a pre-forming of such fingers in the cathode blank would require a high degree of care in later orienting the workpiece during the erosion step, to assure a register of the broach fingers with the slits in the cathode blank, it is preferable to provide the cathode fingers simultaneously with the formation of apertures in the two grids.

After completion of the electrical erosion step der scribed, a top view of the cathode appears as shown in FIG. 3. As will be noted, the erosion step has produced grooves or recesses 80, and has involved complete removal of the portions of the sintered body 82 on the outer surface of the cathode, as well as removal of the material of the cathode blank 52 (FIG. 4), at the regions engaged by the fingers of the breaching tool. However, the broaching tool fingers 74 do not extend fully through the composite body made up of the cathode blank material and the sintered body. Thus, there remains at the broached regions a relatively thin body 84 of the matrix Si), the surfaces of which provide active cathode areas. The broaching tool also forms slots 86, 88 in the grids 16, 14, in radi-al register with the recesses 80 in the cathode.

Following the erosion step described, the anode is brazed to the screen grid flange 22, by interposing between the sealing surfaces of the anode and the flange, a suitably metalized and coated insulating ring 28 and BT solder of the type previously described. The anode 10 and the sub-assembly 63 with the sealing ring 28 and solder referred to, are suitably jigged in coaxial relation and heated in an oven for brazing the anode to the subassembly referred to, to provide the anode-cathode-grid sub-assembly 90 shown in FIG. 6.

It will be noted that the last mentioned sub-assembly has an opening 92 at one end communicating with the inner surface of the cathode 1 8. This opening is utilized in coating the inner surface of the matrix body 50 with electron emitting material.

During a coating operation, sub-assembly 96 is supported in a jig 94 mounted for rotation on the axis of subassembly 90. A conduit 96 extending from a reservoir 98 is provided with a nozzle 100 (which may have a plurality of openings), adapted to extend into the interior of the cathode 18.

The coating material dispensed by nozzle 100 may consist of two parts by volume of a coating suspension described in column 3 lines 36 to 65 in U.S. Patent 2,800,446 to M. N. Fredenburgh, issued July 23, 1957, and one part of acetone. The coating suspension referred to, includes the carbonates of barium, strontium 4and calcium suspended in a medium comprising acetone, dibutyl phthalate, and polymeric methyl rnethacrylate. The resultant coating material has a thin cream consistency.

During a dispensing of the coating material by the noz- Zle 100, the jig 94 is rotated at a velocity of from 200 to 1,000 r.p.m. for a period of from one-half to one minute. This rotation of the dispensed coating material, provides a centrifugal force which is supplemented by capillary action, for effectively dispersing the material entirely through the pores of the matrix 50. Applicant has found that the degree of penetration into the matrix pores of the vCoating material is dependent upon the drying time of the solvent (acetone). If this drying time is of the order of one hour, the capillary force is taken advantage of fully and an equilibruim occurs between the forces urging entry of the material into the pores of the matrix, and the forces that oppose such entry, when full entry of the material has taken place. If the forces of entry Aare too great and the equilibrium is overcome in the penetrating direction, material may be lost or sprayed to contaminate the grids. If the forces of entry are not sufficient, full penetration of the cathode is not achieved. The coating composition described has an important drying time characteristic that permits attainment of the aforementioned equilibrium under the conditions specified.

After the coating has dried, the heater sub-assembly is sealed across the opening 92 (FIG. 6). The heater suba-ssembly, as shown in FIG. 1, comprises an insulatingly coated heater coil 20 fixed at one end to conducting rod 34 and at the other end to conducting rod 36. The rod 34 is sealed through -the flanged metallic plate 40 lwhile rod 36 is fixed to flanged member 38. The plate 40 is fixed to the flanged member 38 by means of the insulating plate 42, made of aluminum oxide, for example, and having suitably metalized and coated surfaces for brazing to the plate 40 and flanged member 38. The fixing of these parts may be effected in an oven prior to incorporation of the sub-assembly in the tube structure.

The assembling of the heater sub-assembly in the tube structure involves extending the heater 20 (FIG. l) into the opening 92 (FIG. 6) until the flanged member 38 is seated in flanged member 26. When so seated, the edges 106, 108, are substantially in a plane normal to the tube axis. In this position, the edges referred to are mutually fixed by locally applied heat, such as by heliarc welding.

The interior of the tube is then evacuated to a suitably low pressure through the exhaust tubulation 12, which may be made of copper for example, and the tubulation is then closed as by pinching for providing a cold-welded closure- While it has been mentioned in the foregoing that the matrix 50 may be applied to the inner surface alone of the cathode blank, or to both the inner and outer surfaces thereof, and that in either case, portions of the matrix are removed in an erosion step, it is feasible to practice the invention without removing any portion of the matrix. It is :essential however, that the cathode blank be slitted to provide the fingers 48. Where no portion of the matrix is removed, the coating material applied to the inner surface of the cathode, will become diffused by capillary action throughout the entire matrix body, by passing through the slits between the fingers 48. In

this example where no matrix material is removed, the radial register of the cathode slits with openings in one or more associated concentric grids, is not critical, since substantially uniform emission is produced from the finished cathode throughout the entire continuous outer surface of its active portion. However, in this example simplicity of manufacture is achieved at the cost of a desired beaming action obtained when portions of the matrix are removed, as described in the foregoing.

I claim: 1. -Method of making an electron tube comprising (a) mutually fixing in relatively close spaced relation to a tubular cathode having openings in the side wall thereof bridged by a metal matrix, within a tubular grid, and thereafter (b) dispensing emitting material to the inner surface of said matrix for migration through said matrix to the outer surfaces of said matrix in said openings.

2. Method of making an electron tube comprising (a) mutually xing by oven brazing a tubular cathode blank having pores, and two imperforate tubular grid blanks surrounding said cathode,

(b) ysimultaneously eroding radially registering openings in said grid blanks, and depressions in the outer surface of the cathode blank to provide two grids and beam forming areas on said cathode blank,

(c) fixing by oven brazing a tubular anode to the outermost of said grids,

(d) dispensing electron emitting material to the inner surface of said cathode for migration through said pores to the outer surface of said cathode at said depressions only,

(e) mounting a heater. assembly within said cathode and sealing said assembly across one end of said cathode, thereby closing one end of an envelope for said tube, and

(f) evacuating said envelope through the other end thereof and sealing said other end.

3. Method of making a tubular cathode comprising (a) forming axially extending slits around an axial portion of a metallic tubular cathode blank,

(b) compacting relatively small metallic particles around the entire of lsaid axial portion and bridging said slits,

(c) sintering said particles to form a matrix having 45 cluding a vaporizable thinner in sufficient amount to keep said material in a suciently low viscous state for a time interval long enough to permit said material to fully penetrate said pores.

4. Method of making a cathode-grid subassembly for an electron tube comprising:

(a) forming a closely adhered coaxial matrix of sintered metal particles on an inner wall of a portion of a tubular cathode blank,

(b) mutually xing said tubular cathode blank and an imperforate tube grid blank around the cathode blank,

(c) eroding openings through said grid blank, and

Y (d) eroding openings in said portion of the cathode blank in radial register with said grid blank openings while preserving said matrix from erosion.

5. Method of making a tubular cathode comprising:

(a) forming on a tubular cathode blank a wall portion consisting solely of a sintered metal matrix body having pores of capillary size,

(b) depositing an electron emitting material on said wall portion within said cathode blank and wherein said material includes a Vaporizable thinning liquid adapted to keep said material below a predetermined viscosity for a predetermined interval of time, and

(c) axially rotating said cathode at a predetermined speed for causing said electron emitting material to pass through said matrix body to the'outer surface thereof during said interval of time.

References Cited by the Examiner UNITED STATES PATENTS 2,501,089 3/1950 Pomerantz 313-337 2,543,728 2/ 1951 Lemmens et `al 313-337 2,647,216 7/1953 Brown S13-346.1 2,808,530 10/ 1957 Katz 313-346.1 2,879,429 3/1959 DeSantis et al. 313-293 2,932,759 4/1960 Sheperd 313-337 2,952,789 9/1960 McCullough et al. 313-250 X 2,980,984-v 4/ 1961 Shrader et al 29-25.16 X 3,007,760 11/1961 Knauf et al. 29-25.17 X 3,146,515 9/ 1964 Raglund 29-25 .17

JOHN F. CAMPBELL, Primary Exalitiner.

JOHN W. HUCKERT, Examiner.

ROBERT SEGAL, WHITMORE A. WILTZ,

Assistant Examiners. 

1. METHOD OF MAKING AN ELECTRON TUBE COMPRISING (A) MUTUALLY FIXING IN RELATIVELY CLOSE SPACED RELATION TO A TUBULAR CATHODE HAVING OPENINGS IN THE SIDE WALL THEREOF BRIDGED BY A METAL MATRIX, WITHIN A TUBULAR GRID, AND THEREAFTER (B) DISPENSING EMITTING MATERIAL TO THE INNER SURFACE TO THE OUTER SURFACES OF SAID MATRIX IN SAID OPENINGS. THE OUTER SURFACES OF SAID MATRIX IN SAID OPENINGS. 